Add a generic l10n template for formatting date string and
clean up the previous hack. Now we can redefine the following
parameters in the localized includes.xsl:

<xsl:param name="param-l10n-date-format-YMD" select="'%D %M, %Y'" />
<xsl:param name="param-l10n-date-format-YM" select="'%M %Y'" />
<xsl:param name="param-l10n-date-format-MD" select="'%D %M'" />